Micro-trou noir

Les micro-trous noirs sont de minuscules trous noirs hypothétiques, également appelés trous noirs quantiques ou mini-trous noirs, pour lesquels les effets liés à la mécanique quantique jouent un rôle important. Il est possible que de tels trous noirs quantiques aient été créés dans l'environnement très dense de l'univers primordial, ou au cours de transitions de phases ultérieures : on parle dans ce cas de trous noirs primordiaux. Ils pourraient être détectés prochainement par les astrophysiciens, grâce aux particules qu'ils devraient émettre par rayonnement de Hawking. Certaines théories impliquant des dimensions d'espace supplémentaires prédisent que des micro-trous noirs pourraient être formés à des énergies relativement basses, de l'ordre du TeV (téra-électron-volt) : c'est un domaine d'énergie qui sera accessible aux accélérateurs de particules tels que le LHC (Large Hadron Collider). La médiatisation de cette possibilité a provoqué des inquiétudes parmi la population. Cependan

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Phenomenology of 10(32) dark sectors

Michele Redi

We postulate an exact permutation symmetry acting on 10(32) standard model copies as the largest possible symmetry extension of the standard model. This setup automatically lowers the fundamental gravity cutoff down to TeV, and thus, accounts for the quantum stability of the weak scale. We study the phenomenology of this framework and show that below TeV energies the copies are well hidden, obeying all the existing observational bounds. Nevertheless, we identify a potential low energy window into the hidden world, the oscillation of the neutron into its dark copies. At the same time, proton decay can be suppressed by gauging the diagonal baryon number of the different copies. This framework offers an alternative approach to several particle physics questions. For example, we suggest a novel mechanism for generating naturally small neutrino masses that are suppressed by the number of neutrino species. The mirror copies of the standard model naturally house dark matter candidates. The general experimentally observable prediction of this scenario is an emergence of strong gravitational effects at the LHC. The low energy permutation symmetry powerfully constrains the form of this new gravitational physics and allows to make observational predictions, such as, production of micro black holes with very peculiar properties.

2009

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Black hole bound on the number of species and quantum gravity at CERN LHC

Michele Redi

In theories with a large number N of particle species, black hole physics imposes an upper bound on the mass of the species equal to M-Planck/root N. This bound suggests a novel solution to the hierarchy problem in which there are N approximate to 10(32) gravitationally coupled species, for example 10(32) copies of the standard model. The black hole bound forces them to be at the weak scale, hence providing a stable hierarchy. We present various arguments, that in such theories the effective gravitational cutoff is reduced to Lambda(G)approximate to M-Planck/root N and a new description is needed around this scale. In particular, black holes smaller than Lambda(-1)(G) are already no longer semiclassical. The nature of the completion is model dependent. One natural possibility is that Lambda(G) is the quantum gravity scale. We provide evidence that within this type of scenarios, contrary to the standard intuition, micro-black-holes have a (slowly fading) memory of the species of origin. Consequently, the black holes produced at LHC will predominantly decay into the standard model particles, and negligibly into the other species.

2008

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Femtolensing by dark matter revisited

Sergey Sibiryakov, Wei Xue

Femtolensing of gamma ray bursts (GRBs) has been put forward as an exciting possibility to probe exotic astrophysical objects with masses below 10(-13) solar masses such as small primordial black holes or ultra-compact dark matter minihalos, made up for instance of QCD axions. In this paper we critically review this idea, properly taking into account the extended nature of the source as well as wave optics effects. We demonstrate that most GRBs are inappropriate for femtolensing searches due to their large sizes. This removes the previous femtolensing bounds on primordial black holes, implying that vast regions of parameter space for primordial black hole dark matter are not robustly constrained. Still, we entertain the possibility that a small fraction of GRBs, characterized by fast variability can have smaller sizes and be useful. However, a large number of such bursts would need to be observed to achieve meaningful constraints. We study the sensitivity of future observations as a function of the number of detected GRBs and of the size of the emission region.

IOP PUBLISHING LTD2018

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Trou noir

alt=|vignette|Le disque d'accrétion du trou noir M87* imagé par l'en. Le trou noir lui-même est invisible, au centre de la zone noire centrale. En astrophysique, un trou noir est un objet céleste si

Évaporation des trous noirs

L'évaporation des trous noirs, qui se traduit par le rayonnement de Hawking (dit aussi de Bekenstein-Hawking), est le phénomène selon lequel un observateur regardant un trou noir peut détecter un in

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L'horizon des événements est, en relativité restreinte et en relativité générale, constitué par la limite éventuelle de la région qui peut être influencée dans le futur par un observateur situé en un

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